SAN JOSE — When firefighters arrived Friday evening at the two homes that sit side-by-side on Linkshead Court, not far from Millbrook Elementary School on the city’s southeast side, both were burning and there was no way to tell which went up in flames first. “We think it was the one on the left,” said Capt. Mike Van Elgort, a department spokesman. It didn’t matter. They quickly set about extinguishing the fire in both houses.

When it was discovered that a gas line had ruptured at one of the houses, the fire was upgraded to three alarms, which brought as many as 60 firefighters. Van Elgort said the cause of the fire is still under investigation, but the fire department does not consider it to be suspicious.

It appeared the blaze began outside — possibly in a rubbish pile between the two homes — and quickly spread to the interiors of the houses, but fire investigators likely won’t make an official determination of its cause for several days, he said.

“The one with the broken gas line we think was the second house on fire,” Van Elgort said. “With a broken gas meter, you have something like a blowtorch, causing the fire to spread much more rapidly.”

The fire left 12 residents displaced, but no one was injured and the damage to both homes was described as moderate. Firefighters rescued three dogs from one house, Van Elgort said. The residents were able to get another dog out of that house on their own.

“Our guys did a great job keeping it to those two homes,” Van Elgort said. “It quite easily could have taken both those houses completely up in flames, and then spread to additional homes because it was a gas-fed fire.”

The Fire Department was alerted to the fire about 6:20 p.m., and the first firefighters arrived on the scene about three minutes later. They had the fire under control by about 7:30, Van Elgort said.

Most residents were away when the fire started, according to Van Elgort. The houses will need to be repaired before residents can move back into them, he said.